1. Field of the Invention
The present invention relates to a lens barrel of a camera, and the like, in which the lens barrel has a plurality of lens frames moving in an optical axis direction, and more particularly, to a lens barrel for firmly coupling lens frames with each other.
2. Description of the Related Art
Conventionally, in lens barrels of zoom lenses, and the like of cameras, lens frames are often coupled with each other through a cam mechanism composed of a cam groove and a cam follower to permit the smooth relative movement of the lens frames in the optical axis direction thereof.
A cam frame, in which the cam groove of the cam mechanism is disposed, is generally molded (injection molded) of a synthetic resin material, and the cross section of the cam groove has inclining surfaces that gradually open outward due to the restriction imposed when a mold is drafted. The cam follower is formed in a conical shape according to the inclining surfaces.
In the coupling of lens frames made by the cam mechanism composed of the cam groove and the cam follower, however, when a user drops a camera by mistake or when some kind or another shock or hit is applied to the camera from forward (from a subject side), there is a possibility that the cam follower gets over an inclining surface of the cam groove and is removed therefrom.
The removal of the cam follower from the cam groove is liable to arise when both the walls of the cam groove have a large inclining angle. When the inclining angle is reduced to make the removal of the cam follower from the cam groove difficult, it is difficult to draft a mold from a molded cam frame. Further, when the diameter of a lens frame is reduced to decrease the size of a camera, it is difficult to draft a mold from a molded cam frame because a gradient lead angle is made tight even if the moving amount of cam lift is unchanged.
To cope with the above problem, Japanese Unexamined Patent Application Publication No. 7-191252 discloses a technology for setting the inclining angle of a pair of confronting inclining surfaces of each of cam grooves to a small angle in a photographing region and to a large angle in a collapsed region and for forming a plurality of taper surfaces on a cam follower according to the inclining angles of the respective cam grooves.
In this conventional art, however, a cam pin must have a plurality of taper angles in a circumferential direction. Thus, when the cam groove is arranged as a non-linear cam groove, the cam pin cannot cover all the regions of the non-linear cam groove, which greatly restricts the employment of the conventional art.
Accordingly, it is an object of the present invention, which was made in view of the above circumstances, to provide a lens barrel in which lens frames are coupled with each other making use of a cam mechanism. The lens barrel has wide versatility, does not make it difficult to mold cam grooves, and can firmly couple the lens frames with each other by the cam mechanism even if unintentional external force is applied to the lens barrel.
A lens barrel has a first frame including a cam groove having a first surface and a second surface that confront each other with the first surface which is not in parallel with the second surface, and has a second frame including a cam follower that has a first outer circumferential surface, which comes into sliding contact with the first surface, that has a second outer circumferential surface, which comes into sliding contact with the second surface at a depth different from that of the first outer circumferential surface in the depth of the cam groove, and that is put between the surfaces which are not in parallel with each other, and the second frame moves relatively to the first frame.
The above and other objects, features and advantages of the invention will become more clearly understood from the following description referring to the accompanying drawings.